As we have just seen in the last chapter, there are 16 elementary switching functions functions with two inputs and one output. Each of the elementary switching functions corresponds to an (elementary) logic function. The logic functions are traditionally given names such as AND, OR, IMPLICATION, etc. that, in this book, are written in capital letters. The switching functions themselves are given the same names as the logic functions — e.g., and, or, implication etc. — only that they are written in lowercase boldface. In this chapter we discuss all the elementary switching and logic functions, and how they correspond to one another. But, apart from the elementary logic functions (that have two inputs), we shall discuss the functions AND, OR, XOR, and EQUIVALENCE for which gates with two and more inputs exist, thus laying the basis for drawing logic circuits.